Three-dimensional (3D) shape extraction technology is an important technology for extracting the 3D shape of an object existing in the real world. And it has already been utilized in many application fields. Technology for extracting the 3D shape of an object may be classified into a contact type and a noncontact type, wherein contact-type 3D shape extraction technology may obtain high-precision 3D measurement data in such a way as to measure 3D coordinates from a measurement region of a target to be reconstructed in a state in which measurement sensors touch the measurement region, but an object that is deformed when pressure is applied or a high-temperature object cannot be measured, and thus noncontact-type 3D shape extraction technology has been presented as an alternative of the contact-type technology.
Noncontact-type 3D shape extraction technology is a scheme for extracting a 3D shape using light reflected or transmitted from an object, wherein in various industrial fields, the development of technology related to systems capable of extracting the 3D shape of a product itself or the surface of the object in a noncontact manner and in real time has been continuously required so as to manage the quality of products.
A photometric stereo technique is a technique for sequentially applying a plurality of lighting units to a target object, and extracting the 3D shape of an object using at least three images acquired by a camera, and is capable of more reliably extracting the 3D shape of an object as the number of lighting units is larger.
Recently, a technique has been developed which applies a photometric stereo technique to three images, obtained by simultaneously radiating light components corresponding to three different wavelength bands of R (red), G (green), B (blue) onto the object by using an RGB camera, and then extracts 3D shape information.
However, since a high-temperature metal object may emit light having a wide frequency band ranging from a yellow light region and a red light region to an infrared region, it is impossible to acquire three or more images having the effect of applying at least three light components which are to be applied to the photometric stereo technique, by using only the above method using the above-described RGB camera and the R (Red), G (Green), and Blue (Blue) light components, and thus it is impossible to extract the 3D shape of a high-temperature material at the present time.
In steel industry, it is very important to extract 3D information about defects on the surface of a high-temperature steel material in a stationary or moving state in the production stage of products, and take suitable actions based on the 3D information from the standpoint of quality management and cost reduction. However, to date, a system for extracting the 3D shape information of an object surface in a noncontact manner and in real time in a high-temperature condition in which an object emits light by itself has not yet been developed, and the development of this 3D shape extraction system is urgently required.